This invention relates to coherent transmission from distributed wireless transmitters. In some examples, these transmitters are access points (APs) in 802.11n wireless network and the receivers are conventional 802.11n clients.
Communication capacities of conventional wireless networks, such as 802.11 or cellular networks, can be limited by interference. For example, the wireless medium is shared, and as a result, if two nearby devices transmit simultaneously, their transmissions typically interfere, preventing either device from delivering its frame. Recent advances in wireless technology have resulted in empirical wireless systems such as Spatial Multiple Access (SAM), Interference Alignment and Cancellation (IAC) and beamforming. These systems have demonstrated that concurrent transmissions across different transmitters in the same interference region are possible. The throughput in wireless networks employing these systems can be doubled or tripled.
However, such systems remain limited by the maximum number of antennas on an individual node, and cannot continuously scale the throughput as more transmitters join the systems. Conventional wireless networks, for example, 802.11 and cellular systems, may alleviate this problem by using all available channels or employing sectorized antennas. However, such techniques provide only a small constant gain that does not scale as the number of users increases. Furthermore, simply adding additional transmitters does not improve user throughput, because these transmitters interfere with each other.
There is a need for a wireless networking system that can scale throughput linearly as the number of users increases, yielding a fully scalable wireless network.